Heat Recovery Booster: Testing Plate Exchanger Efficiency in Waste Heat Upgrader

What is it about?

This study evaluates how well a plate heat exchanger (PHE) works as an "economizer" in a prototype device called a single-stage heat transformer (SSHT), which upgrades low-grade waste heat (like from factories at 60-100°C) into higher-temperature useful heat (up to 150°C) for processes like steam generation or water purification. The system uses a Water/Carrol mixture—Carrol is a lithium bromide blend with additives to prevent clogging (crystallization)—as the working fluid, making it safer and more reliable than standard mixtures. The economizer recovers internal heat by preheating the concentrated solution heading to the absorber using warmth from the returning diluted solution, boosting overall efficiency. Researchers built a compact prototype with stainless steel PHEs for all parts (generator, evaporator, condenser, absorber), ran four steady-state tests at atmospheric pressure, and measured temperatures, flows, and concentrations. They calculated the exchanger's effectiveness (how close it gets to perfect heat transfer) using two methods: the ε-NTU approach (factoring in heat capacities and transfer units) and simple energy balance. Results showed effectiveness of 0.69-0.71, with overall heat transfer coefficients around 0.66 kW/m²K. Simulations revealed that without the economizer, efficiency (COP) drops sharply at higher outputs (e.g., 198% lower at 149°C absorber temp), but with it, the system recovers 30-50% of input heat as useful output. This low-cost, compact design (PHEs reduce size and fluid needs) could recycle industrial waste heat, cutting energy use and emissions in sectors like chemicals or textiles.

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Photo by Kaptured by Kasia on Unsplash

Photo by Kaptured by Kasia on Unsplash

Why is it important?

This research uniquely tests PHEs in SSHTs with Water/Carrol, quantifying 0.71 effectiveness—higher than tube designs—and showing 198% COP gains at high temps, addressing crystallization/corrosion barriers that limit LiBr systems. Timely for post-Kyoto energy recovery, as 20-50% industrial heat is wasted; it enables compact prototypes for desalination (0.1-0.2 L/min water) or cogeneration. Impact: Cuts fuel costs 30-60% with 2-5 year payback, reduces CO2 by tons/site, and scales for renewables like solar (e.g., Mexican geothermal). By validating ε methods, it guides efficient designs, potentially adding GWs of recovered heat globally, aiding water-scarce regions and SDGs on sustainable energy.

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